PHP / Form question

Hello all. I have created a form with the below code. On submit the form call sendmail and sendmail does all the processing.

My issue is when I change themes I also have to change the action. What is the best way to go about this. Should I move sendmail.php to the root? Thank you in advance.

<form method=”post” id=”searchform” action=”http://foo.org/wp-content/themes/dark_maple/sendmail.php”&gt;